Pancreatic Ductal Adenocarcinoma (PDAC) is still a devastating disease that ranks as the fourth leading cause of cancer related death, and its five-year survival remains around 6%. Currently, most PDAC patients are diagnosed with spread or metastasized diseases. In order to change this dismal clinical outcome, the development of novel systemic treatment of locally-spread and metastatic lesions is in need. Oncolytic virus represents one such potential therapeutic modality, and adenovirus (Ad) is a strong candidate because of its efficient in vivo transduction mediated by specific protein-to-protein binding and the exponential replication causing oncolysis. However, even oncolytic adenoviruses (OAds) with the highest infectivity have not yet achieved efficient therapeutic effect upon systemic administration because of non-selective distribution and sequestration by non-target organs. Targeting at the level of viral binding/infection therefore has strong advantages for realizing systemic treatment of advanced cancers. The incorporation of pre-identified ligands in Ad virion has been heavily tried, but inhibition of viral replication or loss of ligand affinity has hampered the realization of the vector in most cases. To overcome this issue, we recently developed a novel ligand for transductional targeting by screening large diversity targeting ligand library (1010 order) in adenovirus format and identified a novel targeting ligand (VTINRSA) against mesothelin (MSLN) that is expressed on the surface of many PDACs. The oncolytic adenovirus (OAd) with this motif (VTIN-OAd) achieved targeted binding and replication in MSLN-expressing cells in vitro as well as selective replication and antitumor effects after intratumoral injection n vivo. The intravenous injection showed significantly lower liver sequestration and better tumor accumulation. More importantly, its intravenous injection exhibited strong antitumor effects in a PDAC subcutaneous xenograft model, even at a low dosage (3x109 vp). The infectivity-selective OAd possesses key properties to embody systemic treatment of pancreatic cancers and thus gives us a unique opportunity to develop novel pancreatic cancer therapeutics that are systemically injectable. The overarching goal of this project is to bring this promising vector ino the clinical stage. The biological/virological backgrounds of the improvement of viral performance upon systemic therapy will be elucidated in vitro and in vivo. We will construct and validate the clinically applicable OAd with this new targeting strategy for systemic therapy of pancreatic cancer. We will also pursue further enhancement of the anti-tumor effect by combining them with chemotherapy. The rigorous tests planned in this proposal will determine the lead OAd and the optimal administration scheme in patients. Successful clinical development of the potent and systemically-injectable oncolytic Ad-based therapy has a high potential to improve the clinical outcome of the patients with unresectable PDAC and other refractory cancers.